Method of making an electrically conductive net-like metal coating



May 30, 1967 c [35 woogy ET Al. 3,322,571

METHOD OF MAKING AN ELECTHICALLY CONDUCTIVE NET-LIKE METAL comma Filed July 18, 1965 INVENTORS CHARLES M. DQWOOOY ROS'GOL L. PEARCE ATTORNEY United States Patent 3,322,571 .METHOD OF MAKING AN ELECTRICALLY CON- DUCTIVE NET-LIKE METAL COATING Charles M. De Woody and Rosco] L. Pearce, Cumberland County, N.J., assignorsto Ace Glass Incorporated,

Vineland, N.J., a corporation of New Jersey Filed July 18, 1963, Ser. No. 296,044 8 Claims. (Cl. 117212) This invention relates to a method of applying an electrically conductive coating to a non-conducting base in the manufacture of conductive elements for items of laboratory glassware and the like, such, for example, as shown and described in copending application Ser. No. 862,331, filed Dec. 28, 1959, and now Patent Number 3,092,704, in which the present applicants are co-inventors. More particularly, the invention consists in new and useful improvements in an electrically conductive element and the method of manufacturing the same, wherein a continuous film-like, molecularly bonded metallic network of random pattern is fused to a non-conducting base or substrate to provide, on the periphery of an article of glassware or other article to be heated, a current distributing resistance band in a complete electric circuit.

conventionally, in the manufacture of heated vessels employing metallic films, a metallo-organic compound including a suitable metallic resin incorporating metals such asplatinum, nickel, etc. is mixed with such solvents as turpentine or other varnish-type solvents, and either sprayed upon the surface to be treated, or such surface is dipped in this mixture, which is then baked to provide a metallic resistance coating. It has been found that with such a coating, While there appears to be a continuous film covering the surface of the base, under sufficient magnification, a semblance of grain-like lines appears throughout, and when the film is subjected to a current amps, for example, (for a film .0005 inch thick) under microscopic examination, it is found that the film breaks away at the grain lines and disintegrates with a resultant peeling off. This is a progressive disintegration, and after a time, failure and burnout occur because the current is progressively directed through narrowing paths, causing hot spots.

It is therefore the primary object of the present invention to overcome these disadvantages experienced with coatings of conventional metallo-organic compounds, by adding to the conventional solution, a suitable quantity of a material having the property of producing voids upon evaporation, decomposition or chemical reaction, which,

' when the coating is completed, provides a continuous metallic network which is fused to the non-conducting base.

Another object of the invention is to provide a continuous network which, when fused to a non-conducting base, is expandible and contractible with the base under elevated temperatures, so as to accommodate the conditions of strain which occur at the substrate interface.

With the above and other objects in view which Will appear as the description proceeds, the invention consists in the novel features herein set forth, illustrated in the accompanying drawings, and more particularly pointed out in the appended claims.

Referring to the drawings:

FIG.'1 is a magnified view diagrammatically illustrating a fragment of a conventional metallic conductive coating;

FIG. 2 is a similar view illustrating the disintegration of such coating under heat conditions; and

FIG. 3 is a magnified view showing a fragment of the metallo-organic coating of the present invention.

Briefly, in accordance with the present invention, a suitable quantity of a material such as a silicone oil which has the property of levelling and is not completely com- 3 ,322 ,5 71 Patented May 30, 1967 patible with the combination solvent and resin used in the compound is added to the conventional metalloorganic compound in solution. The efiect of this coating, when subjected to heat (even room temperature), is that the normal solvent, such as turpentine, evaporates, while the silicone oil which has a much higher boiling point, tends to form a series of globules around which the resin sets. Thus, upon the application of additional heat to the extent necessary to vaporize the silicone oil in the globules, the coating of the resin surrounding the dispersed globules tends to open up and permit the escape of the silicone oil vapor. As a result, there is formed a net-like metallic film or coating overlying and fused to the surface of the container or substrate. The usual terminals and contacts employed in electrically conductive elements of this nature complete the circuit throughout the network and provide a highly effective resistance coating which is expandible and contractible with the base when the unit is heated.

More specifically, in practising one form of the invention, we added to a conventional metallo-organic compound of platinum mixed in solution with the usual solvent such as turpentine, 5% of dimethyl silicone and the resultant solution was applied to a glass base. This formed on the base or substrate a film-like coating approximately .0005 inch thick which was left at room temperature for a sutficient length of time for the normal solvent to evaporate. The added silicone diluent caused a levelling of the coating and, at the same time, inasmuch as the silicone was not, completely compatible with the combination solvent and resin used in the compound, and as the silicone oil had a much higher boiling point than the normal solvent, a series of globules were distributed throughout the coating, around which the resin tended to set during the room temperature evaporation of the initial solvent.

The coating was then subjected to a temperature of approximately 450 F. for a sufficient length of time to vaporize the silicone oil in the globules, causing the coating surrounding the globules to open up and permit the escape of vapor. Thereafter, the coating was subjected to increased temperatures up to approximately 1100 F. At a temperature of 800 F., the organic oxidation began to take place, leaving deposited a metallic network as the oxidation was completed (950l000 F.), and when the deposition on the base had reached a temperature of 1100 F., the metallic network was adequately fused to the base. It should be understood that the actual fusing to the base is a time-temperature function. Ultimate temperatures as low as 1025 F. may be employed with platinum alloys, but higher temperatures are preferred.

Referring to FIG. 1 of the drawings, the conventional coating 5 is typical of a metallic film formed from a standard metallo-organic compound and grain-like lines are indicated diagrammatically at 6. While the actual cause of these so-called grain-lines is not fully understood, one possible cause is the non-uniform oxidation of the organic material of the coating and the inability of the coating to accommodate stresses and strains caused by differential expansion of the coating and the glass base. Another cause may be a flake-like crystal deposition with the formation of natural boundary lines.

In any event, while platinum metals are ductile, there is a failure to accommodate the stresses involved from differential expansion at a comparatively low value when electric current is passed through the film. For example, such a conventional film might tolerate a maximum current of 5 amps.

FIG. 2 shows the same coating on which the grain-lines have caused a peeling or breaking away as at 6a, ultimately leaving bare substrate areas 6b.

FIG. 3 shows the coating of the present invention wherein the continuous network 7 of metal concentration is defined by a series of voids 8 formed by the evaporation of the insoluble or partially soluble phase, as previously described.

The resultant network of metal embodied a continuous random pattern fused to the non-conducting base which, when energized by means of suitable contacts, completed an electrical circuit to effect a uniform distribution of heat throughout the conductive element. As before indicated, this film-like network tends to expand and contract with the base under heat conditions and provides a very effective conductive or resistance coating.

It will be understood that the heat employed in fusing the metallic deposition on the base, depends upon the nature of the substrate but should be as high as possible without significantly deforming the substrate.

While dimethyl silicone has been specifically referred to above, it is to be understood that other materials may be employed if they have the properties of producing the necessary voids in the final coating. For example, high boiling esters such as phthalates, sebacates, etc. may be used. Also, While we have specified 5% as a proportion of silicon oil in the mixture, such proportion of diluent may range from 1-6% in an effective coating.

The foregoing description relates primarily to the use of diluents which are not completely compatible with the combination solvent and :resin and which subsequently vaporize to leave the network coating. It is also within the spirit of this invention to employ other materials such as foaming agents or blowing agents. For example, suit-able quantities of urethane foams, polystyrene foams, etc. may be added to the metallo-organic compound with the result that the necessary voids are produced in the coating to form a network film. Blowing agents such as organic carbonates may also be used which, when heated, give off gas to produce the necessary voids.

It may also be noted that the conductive coating of the present invention has also been found effective in coating distilling columns or thermos-type flasks because of its heat reflecting properties. In other words, when this coating is applied to the external surface of a distilling column or thermos flask, even without the application of electrical current, the coating reflects heat internally of the column or flask.

From the foregoing, it is believed that the invention may be readily understood by those skilled in the art without further description, it being borne in mind that numerous changes may be made in the details disclosed without departing from the spirit of the invention as set forth in the following claims.

We claim:

1. A method of making an electrically conductive element, comprising admixing with a solution of an organometallic resin, an incompletely compatible diluent of higher boiling point than the solvent of said solution, applying a film-like coating of said mixture to the surface of a nonconducting base, evaporating the solvent to set the film, leaving a series of randomly dispersed globules of said diluent, heating said dispersion to vaporize said globules, leaving a continuous porous network of molecularly bonded electrically conductive metal, and fusing said network to said base.

2. A method as claimed in claim 1, wherein the diluent employed has levelling properties.

3. A method as claimed in claim 1, wherein said diluent comprises a silicon oil.

4. A method as claimed in claim *1, wherein the diluent employed is dimethyl silicone.

5. A method as claimed in claim 1, wherein said mixture includes from 1-6% diluent.

6. A method as claimed in claim 1, wherein said mixture contains 5% diluent.

7. A method as claimed in claim 1, wherein the material admixed with said vehicle solvent system consists of a foaming agent.

8. A method as claimed in claim 1, wherein the material mixed with 'said vehicle solvent system comprises a blowing agent.

References Cited UNITED STATES PATENTS 3,189,482 6/1965 Bajars et al 117-227 ALFRED L. LEAVITT, Primary Examiner.

WILLIAM J. JARVIS, Examiner. 

1. A METHOD OF MAKING AN ELECTRICALLY CONDUCTIVE ELEMENT, COMPRISING ADMIXING WITH A SOLUTION OF AN ORGANOMETALLIC RESIN, AN INCOMPLETELY COMPATIBLE DILUENT OF HIGHER BOILING POINT THAN THE SOLVENT OF SAID SOLUTION, APPLYING A FILM-LIKE COATING OF SAID MIXTURE TO THE SURFACE OF A NONCONDUCTING BASE, EVAPORATING THE SOLVENT TO SET THE FILM, LEAVING A SERIES OF RANDOMLY DISPERSED GLOBULES OF SAID DILUENT, HEATING SAID DISPERSION TO VAPORIZE SAID GLOBULES, LEAVING A CONTINUOUS POROUS NETWORK OF MOLECULARLY BONDED ELECTRICALLY CONDUCTIVE METAL, AND FUSING SAID NETWORK TO SAID BASE. 